Large arrays of loudspeaker enclosures have been standard for producing high sound pressure levels for concert production and performance installation for several decades. In that time a variety of array configurations have been developed. In the last decade the preferred large array has evolved into a single vertical array of enclosures referred to as a line array. Similar linear arrays may also be mounted horizontally, but are not referred to in the field as line arrays.
As the complexity of the loudspeaker enclosure has increased, there has been a shift in terminology in reference to the complete assembly. Each loudspeaker assembly may comprise audio transducers, enclosures which define volumes of air for related low and mid frequency transducers, horns or wave shaping sound chambers and related transducers, rigging hardware (often referred to as fly hardware), amplifiers, heat sinks, digital signal processing hardware or networking hardware or some combination of these components. Since these assemblies are then joined together to form an array of the desired geometry, functionality and performance, the more sophisticated loudspeaker enclosures are now frequently called array elements.
A person skilled in the art will realize that for the purposes of rigging applications, the terms loudspeaker enclosure and array element are interchangeable and furthermore that rigging concepts that are applied to arrays will find equal utility in simpler rigging applications.
Array elements are generally connected one to another by means of a structurally engineered rigging system attached directly to the enclosure to form the array. Rigging systems are generally comprised of adjustable metal parts allowing the desired angular relationship between the elements of the array to be achieved. The array element angle, defined by the angular relationship between array elements is commonly fixed by the use of locking structural pins.
Rigging systems are required to perform both as a hanging system and a ground stacking system. The hanging function is implemented on the largest arrays with the use of a lifting device attached to an overhead structure such as a roof of a building, a crane or a temporary staging system. The ground stacking function is generally implemented on smaller arrays and the array elements are manipulated manually. The array may be placed on the ground or on the edge of a stage or platform.
A rigging system is assembled from a variety of materials, fasteners and processes such as welding. These assemblies comprise structural load bearing members and are therefore subject to structural engineering certification by an Association of Professional Engineers somewhere in the world. All rigging systems are generally designed to meet the strictest engineering jurisdictions, since any given brand of touring and installation speakers will be used throughout many countries. European jurisdictions, regarded as the strictest, require an eight to one safety factor in the structural design of rigging systems that are used for theatrical and performance applications. Furthermore there are regulatory limitations placed on device connection and locking methods as well as the additional requirement for safety straps.
By comparison to the strict limits for the entertainment industry, the construction industry is required to meet a three to one safety factor for apparatuses such as cranes and scaffolds.
The weight of rigging assemblies can seem out of proportion to the apparent lifting requirement because of the high ratio safety factors applied. Rigging systems therefore add significant weight to array elements.
In order to achieve a curved array, rigging systems are generally devised with two sets of components, a pair of front rigging components mounted near the front of, and one or two back rigging components mounted on or near the back of the enclosure. By this method a stable curved array may be formed.
Array elements are available in two distinct cross sectional shapes: rectangular and trapezoidal. In order to form and adjust a curve with rectangular array elements a space will form between the fronts of the array elements. In this case the front rigging component will be adjustable in length and the back rigging component will be fixed in length. In order to form and adjust a curve with trapezoidal array elements a space will form between the backs of the array elements. In this case the back rigging component will be adjustable in length and the front rigging component will be fixed in length.
The desired array geometry and the required array element angles are most often determined by dedicated simulation software that predicts the likely acoustic behaviour of the array in the listening environment. Based on the simulation software the geometry is optimized prior to array assembly so that when erected (or flown) the individual array elements point at the exact prescribed locations in the listening area creating even sound pressure distribution. Because of the finite length of the array and the geometry of typical listening environments, the shape of the array is always curved and most often the curvature increases toward the lower portion of the array. A precise and predictable angular setting between the elements is therefore essential.
Assembling and erecting (or flying) of line arrays is performed with the following equipment. Typically, a welded metal structure called a rigging frame is lifted from the ground by one or more chain hoists. The array elements are connected to the underside of the rigging frame and the chain hoists are attached to a suitable overhead structure with steel cables. In some cases where the ceiling height ranges between 100 and 200 feet there is a large temporary grid framework erected for the purpose of a performance that will carry both audio and lighting equipment. The grid is suspended in like manner with steel cables. The largest arrays weigh up to 7,000 lbs including the chain hoists and frames used to pick them off the ground.
The elasticity of materials has given rise to safety problems. When stopping and starting chain hoists which are heavily loaded, the stretching of the steel support cables and the flexing of grid materials, combined with the elasticity of the rigging system causes a significant bouncing motion. Several tons will move rapidly up and down a distance of several inches. This is a significant pinching hazard and severely damaged fingers and hands are not uncommon
There are roughly three different categories of methods for flying line arrays as well as ground stacking. The first method consisted of arranging the array elements face down on removable wheeled dollies that form part of the transportation equipment. The back rigging components were first joined together to form a chain. The chain of array elements was then pulled up by the hoists allowing the array elements to be swung into position and the front rigging components joined. The array element angles were established generally by the insertion of locking pins in either the front or back rigging components, as required. This procedure was referred to as a caterpillar and was dominant in the first years of line array implementation. The pinch hazard was limited to the scissor action of the elements as they were closed to join the front rigging component.
The second method is a dangerous variation on the caterpillar method and remains in use today. The practice involves attaching both the front and back rigging components and setting the array element angles while all the array elements are face down on their dollies on the ground. The rigging frame is attached to the top of the array and the chain hoists are connected to the rigging frame. Such an array might reach a length of twenty feet and weigh more than 3000 lbs.
The motors then start lifting the top end of the array. This results in the entire array being supported by the hoists on one end and the floor on the other end in a near horizontal position. While this condition exists momentarily, it is at best precarious and at worst, dangerous. Array elements and rigging components are generally suited to create a vertical array, not to form a horizontal beam.
The third method arose because the caterpillar method was considered by some to be too slow. A new form of dolly became popular where four or more array elements could be stacked in a vertical fashion and secured for transport. All the elements would remain connected at all times and lifted directly from their dolly into the array as a block of array elements. The array element angles are pre-set before lifting and the blocks identified as to their place within the array design. This block is referred to by technicians as a meat pack.
Various methods of establishing the array element angles with metal parts and structural pins have been developed. The attachment of an additional block of elements and the setting of array element angles requires the lowering of the heavy array which has been flown onto another block of elements sitting on the ground. The pinch hazard at the time of this activity is high.
A further problem arises in large curved arrays when the length of the array prevents significant backward tilting of the entire array. The fixed angles of the flown part of the array cannot be moved. The curvature of the lowermost part of the flown array results in the bottom element reaching a forward leaning angle often more than 45 degrees. Attaching further meat packs can be quite hazardous. Presently it is common to see technicians attach a pack of four array elements by the two front rigging components and then tip over the pack, which weighs more than 900 lbs, as it sits on its dolly. The array is then lowered by the hoists until the back rigging component can be joined to the tilted pack and then it is lifted from the ground.
Ground stacking can be achieved either by the placement of a block of elements on an elevated surface with a forklift which is common in shows that take place in arenas or manually lifting the elements into a stack. Ground stacks are typically four to six elements high.
In a time constrained touring environment the nature of the performance space in generally known in advance and, where possible, the software simulation will be run in advance of arrival at the venue. Once the desired array element angles are known, the required adjustment of the angles must be performed quickly and efficiently so as not to cause a delay in the commencement of array assembly.
The best practice today allows the setting of array angles in the rigging components before the flying process begins. After the process of assembly begins, technicians are still required to reach into a hazardous location and insert structural load bearing pins into the rigging components to structurally secure the weight of the array.
This process requires numerous people to move and position the blocks of elements placing their hands in a dangerous location to finalize the structural connection. This takes significant time and care raising the potential for delays in the already time constraining touring environment. All rigging systems suffer from these limitations in one form or another.
A further safety hazard is found in the lowering of arrays after the performance. The significant weight of the flown array must be lowered carefully to relieve the weight from the structural locking pins that connect the array elements allowing the release and removal of the pins. Since the rigging components are most often found on or near the ends of the array element, a coordinated effort between two technicians is required to remove the pins and to lower the elements their resting position. During this phase a continued pinch hazard exists.
In addition to the procedural and safety limitations of the state of the art rigging systems, numerous other limitations still exist.
Even though significant safety margins are observed, during transport and moving from the truck to the venue, damage may occur. Blocks of array elements are heavy, are often subjected in the concert environment to forklift activity and the array components are generally mounted on the exterior of the array element. In addition to simple physical damage, wear and tear, array element flexural stress and misuse, result in rigging components that do not fit properly. Poor fit results in extensive time loss and increased safety hazard.
Distortions in rigging components are not easily repaired while travelling from one city to another in a touring environment. Often repairs will be left undone and a variety of stop gap measures will be employed to make the array fit together. This work is carried out in an environment where the historical maxim is that the show must go on.
It is an object of an aspect of the invention to mitigate or obviate at least one of the above-described disadvantages of the prior art.